This section provides background information related to the present disclosure which is not necessarily prior art.
Start-up issues, particularly at full load and a low ambient temperature, are known to power supply designers. For example, NTC thermistors are commonly used as an in-rush current limiter to reduce the likelihood of tripping a fuse or damaging the power supply unit component parts. NTC thermistors are designed such that their resistance drops as the device heats up. If the resistance of the NTC thermistor is too high at start-up, e.g. if the ambient temperature is particularly cold, a high voltage drop at the PFC stage output may prevent the power supply unit from powering up and functioning properly.
It is known to delay starting the PFC circuit until the bulk storage capacitor is fully charged. This results in the NTC thermistor heating up and its resistance dropping during charging of the bulk storage capacitor. This allows the NTC thermistor resistance to drop sufficiently to allow the power supply unit to properly power up; however, the time necessary to charge the bulk storage capacitor may be unacceptably long. For example, see the background of U.S. patent application publication US2013/0223120.
It is also known to actively control in-rush current as opposed to the passive control of the NTC thermistor. However, active control requires more component parts and may increase the cost of the PFC circuit and power supply unit.